NREL Develops Switchable Solar Window

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Scientists at the U.S. Department of Energy’s National Renewable Energy Laboratory developed thermochromic windows capable of converting sunlight into electricity at a high efficiency, according to a recent release. Officials say the technology could have architectural applications.

The NREL-developed demonstration device allows an average of 68 percent of light in the visible portion of the solar spectrum to pass through when it’s in a transparent, or bleached, state. When the window changes color—a process that took about 3 minutes of illumination during testing—only 3 percent is allowed through the window.

“There is a fundamental tradeoff between a good window and a good solar cell,” says Lance Wheeler, a scientist at NREL. “This technology bypasses that. We have a good solar cell when there’s lots of sunshine and we have a good window when there’s not.”

The new technology responds to heat by transforming from transparent to tinted. As the window darkens, it generates electricity. The color change is driven by molecules that are reversibly absorbed into the device. When solar energy heats up the device, the molecules are driven out, and the device is darkened. When the sun is not shining, the device is cooled back down, and the molecules re-absorb into the window device, which then appears transparent.